Air foil bearings are a type of hydrodynamic bearing in which a shaft is supported by a compliant, spring-loaded foil that lines a bearing sleeve. When the shaft spins at a high speed, the rotation of the shaft pulls air into the bearing via viscosity effects and forms a high pressure air gap that separates the shaft from the foil such that they do not touch each other.
In the typical air foil bearing, the radial clearance between the foil and the shaft is uniform along the circumferential direction when the bearing is not loaded. When uniform clearance is used, however, the bearing causes the shaft to be dynamically unstable at high speeds. It would be desirable to have an air foil bearing that does not cause such shaft instability.